1. Field of the Invention
This invention relates generally to external combustion expander-type engines. More particularly, the present invention relates to an external combustion expander-type engine having an asymmetrical shaped cam to convert piston linear reciprocating motion to shaft rotational motion.
2. Description of the Prior Art
It is known to propel a torpedo with a propulsion system which uses an external combustion expander-type engine in conjunction with a monopropellant fuel. The inventor of the present device, Duva, discloses such a system in U.S. Pat. No. 5,253,473. In this type of system, a solid initiator monopropellant fuel is combusted in the combustion chamber, producing a hot, energized gas which commences drive action of the torpedo and initiates the entry of a liquid, pressure-sensitive, sustainer monopropellant fuel into the combustion chamber through a poppet valve. Assuming that the pressure in the combustion chamber is sufficiently high, heat generated in the combustion of the initiator propellant effects combustion of the initial quantity of sustainer propellant which is admitted to the combustion chamber. Subsequently, combustion of the sustainer fuel continues in a self-sustaining manner due to the high temperature and pressure in the chamber, i.e. part of the energy generated in combustion of the sustainer propellant is used to combust additional sustainer propellant.
In a conventional external combustion engine, the pistons are parallel to the output drive shaft of the engine. The linear reciprocating motions of the pistons are converted to rotational motion of the drive shaft via a swashplate or a cam. The pistons derive their energy for axial motion from the high-energy gas expelled from the combustion chamber. Typically, the process occurs in a sequential manner for each cylinder and generates a reaction force parallel to the center line of the engine. The sequential nature of the reaction forces gives rise to rocking moments about the engine center line. In addition, the high-pressure gas is transferred to the cylinders through hot gas transfer channels. The high-pressure gas flowing through the channels generates flow noise proportional to the velocity and flow rate of the flowing gas. The combination of flow noise and noise generated by the rocking moment can be disadvantageous to the extent that such noise facilitates discovery of the location of the torpedo and the launching vessel.